1. Field of the Invention
The present invention relates to a vehicle navigation system and a method of generating updated map data for the vehicle navigation system.
2. Description of the Related Art
In recent years, a vehicle navigation system, which receives positional information of a current traveling position of a vehicle from satellites and displays the positional information of the vehicle on a display together with map information to navigate a user, has been put into practical use. Further, the vehicle navigation system displays icons indicating various kinds of facility on the display together with a road map. Map data including the road map and facility information is utilized by the vehicle navigation system as a map database in a stored state in a storage medium or a storage device. The map database is realized by a HDD (Hard Disc Drive) in addition to a CD (Compact Disc)-ROM (Read Only Memory) and a DVD (Digital Versatile Disc)-ROM into which the map data is stored. Then, when the HDD stores the map data, the stored map data can be replaced with updated new map data. Although the user can know the latest map information by the updated map data, there is a problem that the map information may not be appropriate for making an accurate decision if it is hard to recognize whether the map information displayed on the display is updated or not.
For such a problem, Japanese Patent Laid-Open No. 2002-188926 suggested a technology as described below. Japanese Patent Laid-Open No. 2002-188926 suggests a navigation system that readily transmits updated map information (second map data) to the user when old map information (first map data) is updated by difference information or the like. According to the navigation system, it is possible to readily transmit updated map information to the user by displaying map information based on data, which was detected by a difference data detecting section, in an emphasized manner or by providing the information in an emphasized manner. Further, in Japanese Patent Laid-Open No. 2002-188926, the detail level of emphasis display is determined depending on usage characteristics that a map data usage characteristics learning section learned. This makes it possible to change the detail level of contents to be shown to the user depending on use frequency, such that the detailed contents of updated map information around a road that the user frequently uses is shown to the user. Furthermore, with the suggested technology of Japanese Patent Laid-Open No. 2002-188926, it is possible to select or specify map information that the user wants to acquire from outside. As described, by updating only map information that the user needs, the data capacity that the navigation system can store can be controlled.
However, in the case where a user who does not know that a facility was changed to another facility tries to search for the facility before the change, the suggested technology of Japanese Patent Laid-Open No. 2002-188926 does not include a function capable of searching for a target facility. So, the suggested technology of Japanese Patent Laid-Open No. 2002-188926 is unable to provide the user with a useful search result in such a situation. Further, in the suggested technology of Japanese Patent Laid-Open No. 2002-188926, the detail level of emphasis display is determined depending on the use frequency, but it is not always necessary to display updated facility information around a road that the user has never used, for example, in an emphasized manner even if it was updated. This is because the user only comes to know a facility around the road, which he/she has never used before, for the first time after the update. In many cases, it is not inconvenient for the user even if he/she does not know what the facility was before the change. Herein, Japanese Patent Laid-Open No. 2002-188926 exemplifies a mode of emphasis display where a road before a change and a road after the change are simultaneously displayed as a mode of emphasis display in Embodiment 1. However, map information before an update is needed in order to execute emphasis display in such a mode. For this reason, in the suggested technology of Japanese Patent Laid-Open No. 2002-188926, map information after an update must be stored in a storage medium together with all corresponding map information before the update. Furthermore, the detail level of emphasis display can be changed depending on use frequency in the suggested technology of Japanese Patent Laid-Open No. 2002-188926, but even if it is possible not to display the map information before an update by the detail level of emphasis display, such information is not simply displayed. In other words, from the above-described viewpoint, since even the map information after an update, whose emphasis display is not necessary, must be stored together with the map information before an update, the data capacity is increased by the map information after the update. In addition, with the suggested technology of Japanese Patent Laid-Open No. 2002-188926, map information that the user wants to acquire from outside can be selected or specified, but it is difficult to make the user select or specify whether or not to acquire map information of a facility around a road that he/she has never used before, for example, and it is not very convenient even if it is possible.